BEIJING — Since the beginning of winter, many Chinese cities, including the capital, have repeatedly been shrouded in air pollution. But the horrendous air quality not only depresses people: It is literally driving more and more of them to pack up and leave China's booming coastal cities, and even to consider emigration.

The latest Hurun Report of the richest Chinese showed that fleeing from environmental pollution is now one of the three top reasons cited by China's wealthy for leaving the country for good. Though studies on a direct relationship between environmental pollution and international migration are so far limited, two Singapore university professors' findings offer a good glimpse into the issue. Based on research from 153 large cities, and from the "migration" search index of Baidu — China's largest search engine — it is clear that the more serious the air pollution, the higher the positive correlation with online searches using keywords related to emigration.

Using the daily Air Quality Index (AQI) published by the 153 cities, the researchers found out that when air quality worsens, search keywords like "mask," "haze" and "PM 2.5" (particulate matter) appear — going up by 10.3 to 12.7%, 19.5 to 27.1% and 23.3 to 32.1% respectively. Meanwhile, every time a city's AQI increases by 100 points, its residents' search index on topics around emigrating goes up by 2.3-4.7% the next day.

The effect of air pollution on emigration-linked searches thus seems to be much lower than on keywords like "mask" or "haze." But this is understandable, since only the richest Chinese people can possibly regard leaving the country as one of their options, while nearly everybody can afford to buy a mask.

Meanwhile, air pollution also seems to affect Chinese major cities' dwellers differently: Beijingers exhibit the strongest desire to flee air pollution, while people in Shanghai, Guangzhou and Shenzhen appear less distressed. One possible reason is that pollution in Beijing is comparatively much worse than in the other three mega-cities.

Although settling down in a foreign country is a long-term decision, the far-reaching impact expressed by this newfound interest in emigration is not to be ignored. Both brain drain and capital flight are to the exporting country's disadvantage. In general, career perspectives and income discrepancy are the major reasons driving people to leave. Now in China, we are beginning to learn the weight on the future of these new "environmental migrants."